As Scott Roberts said, 2.750 is common in current top fuel applications, 10,000 HP+ and 10,000 RPM's. But that's not the entire story of course. These main sizes are housed in a structural cage, a deep skirt, cross bolted arrangement. Most all of these blocks have 9/16" main bolts, very long and deep into the block. The cross bolts are 1/2" minimum. Some have a 5/8", 9/16" combination of fasteners set deep into the structure of the block. The goal is to provide a straight tunnel for the crankshaft to turn in under load. No way that's going to happen with the heaviest load being imparted to an unsupported section of the block just hanging out in the oil pan. We do the best we can with what we have. I will never be convinced it's the best for maximum HP. I love Pontiac's but they were never designed for 3000+ HP. None of these stock block designs were. That's why clean sheet of paper billet blocks exist. It's nostalgia, pure and simple.
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